Acta Geochimica (v.31, #3)
Geochemical characteristics and metallogenesis of Carlin-type gold deposits in the Sandu-Danzhai metallogenic zone, Guizhou Province, China by Baowen Yan; Yong Xia; Zepeng Wang; Qingping Tan; Shourong Wu; Erchuan Fan (209-220).
Geochemical studies of the Paiting and Miaolong Carlin-type gold deposits in the Sandu-Danzhai metallogenic zone, Guizhou Province, have shown that the mineralized-altered rocks show LREE-enrichment patterns, generally displaying negative Eu anomalies (δEu=0.51–0.97) and unobvious negative Ce anomalies (δCe=0.86–0.99). Calcite and fluorite in relation with metallogenesis show MREE-enrichment patterns, generally displaying rather weak negative Eu anomalies (δEu=0.74–0.93) and weak negative Ce (δCe=0.70–0.98) anomalies. The δ13CPDB values of carbon in calcite are −1.61‰–−5.82‰, the δ18OSMOW values of oxygen are 13.97‰–19.24‰, and the δ34SCDT values of sulfur in stibnite are 17.72‰–21.68‰. In regard to δD and δ18O, ore-forming fluids possess the characteristics of metamorphic water. The process of metallogenesis of the Carlin-type gold deposits is controlled by the Yanshanian tectonic activities. The Yanshanian movement promoted the migration and mobilization of metamorphic fluids in the extensively developed medium-to high-grade metamorphic rocks in this region, carrying primarily enriched gold and associated elements such as Hg, As, and Sb in the Sinian metamorphosed black shales and Lower Cambrian black shales. The ore-forming fluids found their way into a suitable metallogenic environment along the fault zone, followed by gold precipitation to form gold deposits.
Keywords: carlin-type gold deposit; geochemistry; Paiting and Maiolong gold deposits; Guizhou Province
Geochemistry and petrogenesis of Neoproterozoic A-type granites at Nakora in the Malani Igneous Suite, Western Rajasthan, India by Naresh Kumar; G. Vallinayagam (221-233).
The Nakora Ring Complex (NRC) (732 Ma) occurs as a part of Malani Igneous Suite (MIS) in the Western Rajasthan, India. This complex consists of three phases (volcanic, plutonic and dyke). Geochemically, the Nakora granites are peralkaline, metaluminous and slightly peraluminous. They display geochemical characteristics of A-type granites and distinct variation trends with increasing silica content. The peralkaline granites show higher concentrations of SiO2, total alkalies, TiO2, MgO, Ni, Rb, Sr, Y, Zr, Th, U, La, Ce, Nd, Eu and Yb and lower concentrations of Al2O3, total iron, Cu and Zn than metaluminous granites. AI content is ≥1 for peralkaline granites and <1 for peraluminous and metaluminous granites. Nakora peralkaline granites are plotted between 4 to 7 kb in pressure and are emplaced at greater depths (16–28 km and 480–840°C) as compared to metaluminous granites which indicate the high fluorine content in peralkaline granites. The primitive mantle normalized multi-element profiles suggest that Nakora granites (peralkaline, metaluminous and peraluminous) are characterized by low La, Sr and Eu and relatively less minima of Ba, Nb and Ti which suggests the aspects related to crustal origin for Nakora magma. The Nakora granites are characterized as A-type granites (Whalen et al., 1987) and correspond to the field of “Within Plate Granite” (Pearce et al., 1984). Geochemical, field and petrological data suggest that Nakora granites are the product of partial melting of rocks similar to Banded Gneiss from Kolar Schist Belt of India.
Keywords: trace element; REE; petrogenesis; Malani Igneous Suite; Nakora; Rajasthan
Background deduction of the Chang’E-1 gamma-ray spectrometer data by Liyan Zhang; Chunlai Li; Jinazhong Liu; Yongliao Zou; Ziyuan Ouyang (234-241).
Gamma-ray spectrometer (GRS) is used to detect the elemental abundances and distributions on the lunar surface. To derive the elemental abundances, it is vital to acquire background gamma rays except lunar gamma rays. So GRS would observe background spectra in the course of earth-moon transfer on schedule. But in fact, GRS was not switched on in the course of flying toward the moon. After the CE-1 probe finished one-year mission, GRS carried out a test on background data on November 21–22, 2008. The authors did conduct research on the methods of background deduction using 2105 hours of usable gamma-ray spectra acquired at the 200-km orbital height by the GRS and more than 5 hours of gamma-ray spectra acquired in the GRS background test. The final research results showed that the method of deducting the background using the minimum counts in the CE-1 GRS pixels is optimal for the elements, U, K and Th. The method applies to such a case that the elemental abundances in the pixel with the minimum counting rate are 0 μg/g and the continuum background counts are constant over the Moon. Based on the method of background deduction, the full energy peak counts of U, K, and Th are calculated.
Keywords: Chang’E-1; gamma-ray spectrometer; lunar gamma ray; background deduction
Geochemistry of the uranium-thurium-bearing granitic rocks and pegmatites of wadi haleifiya area, southeastern Sinai, Egypt by R. I. El Gharbawy; W. M. El Maadawy (242-259).
There are two main granitic rocks cropping out in the study area: 1) the syn-orogenic granites are moderately weathered, jointed, exfoliated and characterized by low relief. These rocks are subdivided into tonalite and granodiorite. They are essentially composed of plagioclase, quartz, biotite, hornblende and potash feldspar; and 2) the post-orogenic granites, characterized by high relief terrain and represented by monzogranite, syenogranite and alkali granite. The monzogranites suffered hydrothermal alteration in particular along joints, faults, shear zones and fractures, which recorded the highest values of radioactivity, reflecting the role of post-magmatic alteration processes in the enhancement of radioactivity. The hydrothermal alteration (desilicification and hematitization) resulted in the formation of mineralized (altered) granites. The altered granites are enriched in TiO2, Al2O3, FeOT, MnO, MgO, Na2O, Rb, Sr, Y, Zr, Zn, Ga and Co and depleted in SiO2, CaO, P2O5, Nb, Pb, Cu, Ni and Cr relative to the fresh monzogranite. The investigated granites contain basic xenoliths as well as pockets of pegmatites. Perthites, quartz, plagioclase and sometimes biotite, represent the essential constituents. Some accessory minerals like zircon are metamicted reflecting their radiogenic nature. The alkali granites are characterized by the presence of aegirine, rebeckite and arfvedsonite. Both syn- and post-orogenic granites show some variations in their bulk chemical compositions. The older granitoids are metaluminous and exhibit characteristics of I-type granites and possess an arc tectonic environment. On the other hand, the younger granites are peraluminous and exhibit the characteristics of post-collisional granites.It is interpreted that radioactivity of the studied rocks is mainly controlled by both magmatic and post-magmatic activities. Frequently, the post-orogenic granites host zoned and unzoned pegmatite pockets. Some of these pockets anomalously attain high radioactivity. The syenogranites and the pegmatites are characterized by high contents of SiO2 and K2O and low CaO and MgO. They have transitional characters from highly fractionated calc-alkaline to alkaline. The alkali granites related to A2-subtype of A-type granites. The post-orogenic granites were originated from magma of dominant crustal source materials and related to post-collisional setting under extensional environment.
Keywords: synorogenic; postorogenic; granite; hydrothermal; pegmatite
Effects of temperature and pressure differences on water seepage in breccia by Longjun Xu; Xingmin Wang; Xuefu Xian (260-263).
Effects of temperature and pressure differences on water seepage in breccia were investigated by using the physicochemical seepage instrument. The results show that the relationship of flow and pressure differences can be expressed by a linear equation, and the seepage coefficient is linearly correlated with temperature. The relationship between seepage flow and temperature could be described with the linear equation. The constant and temperature seepage coefficient showed a linear relation with pressure. Binary quantitative equation for the seepage flow, temperature and pressure was obtained, and explained with experimental data and theoretical analysis.
Keywords: water seepage; pressure difference; temperature; breccia
Geochemical characteristics of saturate hydrocarbons in crude oils and source rocks of the Qaidam, Tarim, Tupran basins, NW China by Min Zhang; Philp Paul (264-275).
Based on the systematic analyses of fifteen typical crude oils and ten typical potential source rocks collected from the Qaidam, Tarim and Turpan basins, Northwest China, the geochemical characteristics of the oils and source rocks were investigated and oil-source rock correlations undertaken. The oils and source rocks deposited in saline lacustrine environment from the western Qaidam Basin were characterized by n-alkanes with even carbon-number preference in the C20-C28 range, low pristane/phytane (Pr/Ph) ratios (less than 0.5), and high abundances of C27 steranes, gammacerane and C35 hopanes. The oils and source rocks deposited in marine environment from the Tarim Basin were characterized by n-alkanes with even carbon-number preference in the C14-C18 range, relatively low Pr/Ph ratios (near to 1), high abundance of C28 steranes, and relatively high gammacerane. In contrast, the oils and source rocks deposited in terrigenous bog environment from the Turpan Basin were characterized by relatively high Pr/Ph ratios (oil samples greater than 6) high abundance of C29 steranes, and relatively low gammacerane and C31–35 hopanes. The higher amounts of C37 and C38 n-alkanes of source rocks from the western Qaidam Basin and the Tarim Basin suggest an origin of these alkanes from functionalized C37 and C38 n-alkadienes and alkenones in prymnesiophytes living in lacustrine and marine environments. Oil-source rock correlations suggest oils in the western Qaidam Basin were derived from the Oligocene Lower Ganchaigou Formation (E3), oils in the Tabei and Tazhong uplifts from the Tarim Basin have a genetic relationship with the Middle-Upper Ordovician source beds. Oils in the Turpan Basin generally fall into two genetic types. Most oils in the Taibei depression from the Turpan Basin were derived from the Lower-Middle Jurassic coal measures, but the fewer oils in this region are a mixed source derived from the Lower-Middle Jurassic coal measure and the Upper Permian source rocks.
Keywords: Qaidam, Tarim, Turpan basins; marine; terrestrial; crude oil; source rock; terpane
Role of asymmetry effect on the specific conductivity of water—A case study by D. Parameswara; K. S. S. Prasad (276-281).
Forty-one water samples in each season (both pre- and post-monsoon) were collected from different formations of the Kadiri schist belt located in the Anantapur district, Andhra Pradesh. The specific electrical conductivity (EC) of these water samples was measured at 25°C by using specific conductivity bridge. The specific conductivity values of the water samples were also calculated by multiplying ionic concentrations with conductivity factor. It is found that the observed EC values of all water samples collected in both the seasons are different from the estimated EC values because of the electro-chemical properties of ions in water.
Keywords: specific conductivity; electro-chemistry; asymmetry effect; electrophoresis effect
Discussion on the interrelationship among Cu-Ni sulfide deposits, mafic volcanic rocks and intrusive rocks in the Sipu region, northern Guangxi, China by Zhenjun Yang; Wenshan Zhang; Jishun Liu; Lijun Yin (282-296).
The Sipu region of North Guangxi is located in the southwest of the “Jiangnan Ancient Land”, where there are developed the oldest stratum in southern China, the Proterozoic Sipu Group, and there are also largely exposed mafic intrusive rocks, mafic volcanic rocks and copper-nickel sulfide deposits. Both mafic intrusive rocks and volcanic rocks are rich in MgO (6.52%–26.39%), but poor in K2O (0.05%–1.00%) and TiO2 (0.33%–0.89%). They are also rich in trace elements such as Rb and Ba while poor in Ta, Nb and the like. Both of them have medium contents of rare-earth elements, 30.26×10−6–126.71×10−6, in which LREEs are slightly rich with ΣLREE/ΣHREE of 1.35–2.46, δEu 0.79–1.33, displaying weak or no δEu anomaly, with the same geochemical features. The right-inclined distribution patterns and the features show that magma would be formed at the comagmatic undiagenetic stage. All studies show that mafic intrusive rocks and volcanic rocks are the products of the same source region evolving in different stages and times. The copper-nickel sulfide deposits are characterized by liquation, crystallization and fractionation of mafic rocks, and have some interrelations with mafic intrusive rocks and volcanic rocks with respect to magmatic genesis.
Keywords: Sipu Group; volcanic rock; intrusive rock; copper-nickel sulfide deposit
Enhanced toxicity of atrazine to Daphnia magna in the presence of nano-CeO2 by Zhaoxiang Han; Jiaying Li; Wei Bao; Jiahong Wang (297-302).
In this study, aquatic toxic effect of atrazine, and nano-CeO2, the accumulation, reproduction and adsorption of atrazine onto nano-CeO2 and the facilitated transport of atrazine into D. magna by nano-CeO2 were examined. The results showed that atrazine concentrations of 3.0, 4.0, and 10.0 mg/L exhibited 43%, 56%, 68% mortalities, respectively, which indicated the mortality was 56% while the concentration of nano-CeO2 was 4.0 mg/L. D. magna accumulated considerably more atrazine when exposed to atrazine-contaminated water in the presence of nano-CeO2. At the same time, atrazine and nano-CeO2 yielded a significant reduction of the reproduction rate at all concentrations tested. What is more, the co-exposure of nano-CeO2 and atrazine was observed to significantly decrease the reproduction rate of D. magna, and atrazine adsorbed on nano-CeO2 quickly. Therefore, attention should be paid to their associations with other contaminants for the risk assessment of nano-CeO2 and it is worthy of notice that the sorption of atrazine on nano-CeO2 would enhance the toxicity of atrazine to D. magna.
Keywords: atrazine; nano-CeO2 ; toxicity; Daphnia magna
HPLC separation of higher fullerenes in the synthetical “graphite smokes” soot by Jun Zhang; Luann Becker; Handong Liang; Yang Luo; Wei Xu; Hongcui Wang (303-308).
Higher fullerenes (C84, C90, C92, C94 and C96) were successfully isolated from the Soxhlet extract of the synthetical “Graphote Smokes” soot (GS sample) by using a big Cosmosil Buckysep (Phenomenex) column (250 mm × 10 mm) with a large injection. The fractions isolated have been determined by high performance liquid chromatography (HPLC) and laser desorption mass spectrometry (LDMS). It is found that there are different fullerenes molecules in different fractions with retention time. The result indicates that fullerenes do exist in GS samples. Also, it excludes the suspicion to some extent that fullerene molecules might be generated by the laser desorption process in the LDMS. In addition, it also provides the experimental basis for the study of natural higher fullerenes and might be helpful to figure out the question if higher fullerenes do exist in the natural samples.
Keywords: higher fullerenes; HPLC; graphite smokes; Soxhlet extract
Isotopic effect of runoff in the Yarlung Zangbo River by Zhiyou Gao; Xiaodan Wang; Guan Yin (309-314).
This paper mainly analyzed the isotopic effect of precipitation in the Yarlung Zangbo River. On the whole, the isotopic compositions of most water samples fall on the upper right of the global meteoric water line. According to δD and δ18O data of the samples, the precipitation equation is figured out as δD=8 δ18O+10, showing that they are derived from precipitation but have experienced intensive evaporation. With obvious region-continental effect (a continuous depletion in heavy isotopes in water bodies occurs with increasing distance from the coast), the water presents a reducing trend of δD and δ18O westwards and southwards. Altitudinal effect is evident here, occurring in both trunk stream and main branches of the Yarlung Zangbo River. The distribution of water isotopic compositions is concerned with the movement of precipitation clouds from the Bay of Bengal and the Nujiang River and is affected by the topographic and climatic conditions of the Tibetan Plateau.
Keywords: runoff; hydrological rule; isotopic composition; Yarlung Zangbo River
Geochemistry and geological significance of the Upper Paleozoic and Mesozoic source rocks in the Lower Yangtze region by Yanran Huang; Zhihuan Zhang; Liyuan Wu; Chunjuan Zang; Qiong Li (315-322).
The Lower Yangtze region is one of the important marine sedimentation areas of oil and gas distribution in southern China, for its favorable source rocks, reservoirs and covers. However, the intense tectonic movements and complex hydrocarbon generation process made it highly impossible to form large-sized oil and gas reservoirs. So it was divided to different hydrocarbon-bearing preservation units in oil-gas exploration. Recent study shows that the Permian and Lower Triassic source rocks in the Lower Yangtze region are complicated in lithology. The hydrocarbon generation potential of limestone there is low while argillaceous source rocks are overall of high abundance with excellent organic types, now in the process of hydrocarbon generation, so differences in high maturity influence the evaluation of organic matter abundance and type. Biomarker characteristics indicate a reductive environment. n-alkanes are marked by a single peak, with no odd-even predominance. The composition and distribution of the carbon numbers of n-alkanes, and the high abundance of long-chain tricyclic terpanes are indicative of marine sedimentation. The high contents of pregnane, homopregnane, rearranged hopane suggest that the source rocks are of high maturity. There is a good linear correlation between methylphenanthrene index and vitrinite reflectance. The correlation of oil-source rocks indicated that the oil of Well HT-3 may come from the Permian Longtan Formation in the Huangqiao area, the oil of Wells Rong-2 and Juping-1 came from the Lower Triassic Qinglong Formation in the Jurong area. The exploration here is promising in those different source rocks which all have great potential in hydrocarbon generating, and oil and gas were produced in the late stage of hydrocarbon generation.
Keywords: high maturity; source rock evaluation; oil-gas correlation; Lower Yangtze region
A study on Pb isotopic characteristics of raw bauxite in western Guangxi, China by Qinzhi Liu; Qianhong Wu; Yiping Zhang (323-326).
The Pb isotopic composition of ores is one of the important approaches to trace the ore sources. It has not yet been applied to research on bauxite ore so far. The current research on bauxite deposits in western Guangxi, China, seldom focuses on raw bauxite and studies on raw bauxite are mostly at macro-level. This study is the first to apply Pb isotope data to tracing bauxite ore sources. The Pb isotopic compositions of ore and rock samples from the Nadou and Taiping mining districts are projected on the Doe and Zartman plumbotectonic models and the results showed that the ore resources are different for the two mines.
Keywords: Guangxi; raw bauxite; Pb isotope; ore source
The origin and accumulation model of crude oils from oil reservoirs Chang 9 and Chang 10 in the Yanchang Formation of the Ordos Basin by Junping Huang; Xiangbo Li; Qilin Chen; Zhanlong Yang; Yanrong Wan; Lihua Wei; Liwen Long; Xiaoguang Liu (327-339).
In the lower parts of oil reservoirs Chang 9 and Chang 10 of the Yanchang Formation are oil-bearing layers newly found in oil exploration in the Ordos Basin. Based on GC, GC-MS analyses of saturated hydrocarbons from crude oils and source rocks, reservoir fluid inclusions and BasinMod, the origin of crude oils, accumulation period and accumulation models are discussed in combination with other petroleum geology data in this paper. The result shows that (1) there are two different types of crude oils in oil reservoir Chang 9 in the Longdong and Jiyuan regions: crude oils of type I(Well D86, Well A44, Well A75, Well B227, Well X62 and Well Z150) are mainly derived from the Chang 7 source rocks (including mudstones and shales) and distributed in the Jiyuan and Longdong regions; those of type II(Well Z14 and Well Y427), are distributed in the Longdong region, which are derived from the Chang 9 source rocks. Crude oils from oil reservoir Chang 10 in the Shanbei region are mainly derived from the Chang-9 source rocks; (2) there are two phases of hydrocarbon filling in oil reservoir Chang 9 in the Jiyuan and Longdong regions and oil reservoir Chang 10 in the Shanbei region: The first phase started at the early stage of J2z. The process of hydrocarbon filling was discontinuous in the Late Jurassic, because of the tectonic-thermal event in the Ordos Basin. The second phase was the main accumulation period, and hydrocarbons began to accumulate from the late stage of J2a to the middle-late of K1, mainly at the middle-late stage of K1; (3) there exist two types of accumulation models in oil reservoirs Chang 9 and Chang 10 of the Yanchang Formation: source rocks of the reservoirs in oil reservoir Chang 9 in the Jiyuan region and oil reservoir Chang 10 in the Shanbei region, the mixed type of reservoirs on the lateral side of source rocks and source rocks of the reservoirs in oil reservoir Chang 9 in the Longdong region.
Keywords: oil-source correlation; accumulation model; oil reservoirs Chang 9 and Chang 10; Ordos Basin
Relationship between the geochemistry of organic matter and the generation of palygorskite in Jiangsu-Anhui border and Gansu Province, China by Chuanping Chen; Yaping Xu; Xiaotian Wang; Yeling Jin; Jing Chen (340-346).
Soluble organic matter had been separated from several palygorskite and bentonite samples in the Jiangsu-Anhui border area (across Jiangsu Province and Anhui Province) and Linze County in Gansu Province of China and was analyzed with the techniques and methods of organic geochemistry. The composition and distribution of hydrocarbons were analyzed by gas chromatography (GC). Organic stable carbon isotopic ratios (δ13C) in typical samples were determined. The abundance of soluble organic matter in all clay samples analyzed was low. In Jiangsu-Anhui samples, the preservation states of organic matter are different; hydrocarbons in organic matter have some features of aquatic plankton but are short of the input of terrigenous higher plants; organic δ13C in a palygorskite of Yongxiaoshan in Xuyi County, Jiangsu Province, is −6.72‰. These features may be typical of a sedimentary environment of closed or semi-closed and relatively isolated different waters near coast or seashore. On the contrary, in samples from Gansu, the preservation states of organic matter are good; the GC graphs of hydrocarbons show that the precursors of the organic matter are from a mixed source of aquatic organisms and land-sourced higher plants; organic δ13C of a palygorskite from Yangtai of Gansu is −15.62‰. It indicated that the sedimentary environment may be an inland salty lake. Preliminary results suggest that palygorskite minerals in the Jiangsu-Anhui area may be evolved from rapidly accumulated fine material or volcanic ash, but clays in Gansu Province may be transformed from terrigenous inorganic clastic components carried to the lake through river and then deposited. The generation process of the samples studied in the paper seems to be related to salty water.
Keywords: palygorskite; organic matter; composition and distribution; generation